Replacement Springs

My rear leafs appear to be worn out: They look pretty flat at the front hanger, and the left side of the truck sits ~1/4" lower than the right. I am trying to determine which springs to replace them with.

I have an aluminum shell over the bed, and I'm working on a built in drawer/platform system. I expect to have at least a few hundred pounds on the bed at all times, and wonder if the additional weight is enough to justify HD springs, or if it would just ride quality and handling. I'm trying to decide between the 4 leaf pack rated at 1,250 lbs and the 5 leaf pack rated at 1,750 lbs I found here. I'll be driving on the highway a lot, and don't plan to do any serious off roading, but plan to be off road, on fire roads, etc, a fair bit.

Any input would be appreciated! Also, does anyone know the rating of the stock springs? I'm guessing it's around 1,100 lbs based on the first option at the linked site.

Oh yeah, that's definitely enough to justify HD springs if you're running that setup constantly. Back when I had a Toyota I replaced the rear leafs with General HD ones and was very happy with them. When I bought my current truck it had Airspring "Air Lift" springs already installed, otherwise i'd be putting the HD leafs in. I will say, the air bags ride very nice even unloaded, so that may be another option worth looking into.

I did end up putting in HD springs from ATS, and they are working out great. Definitely not too stiff, and I suspect the only reason they weren't spec'd from the factory, at least for XLTs, was cost. I recommend this upgrade to anyone who's on the fence.